Electro-wetting on dielectric (EWOD) is a well known technique for manipulating droplets of fluid by application of an electric field. It is thus a candidate technology for digital microfluidics for lab-on-a-chip technology. An introduction the basic principles of the technologycan be found in Digital microfluidics: is a true lab-on-a-chip possible?, R.B. Fair, Micofluid Nanofluid (2007) 3:245-281.
U.S. Pat. No. 6,565,727 (Shenderov, issued May 20, 2003) discloses a passive matrix EWOD device for moving droplets through an array.
U.S. Pat. No. 6,911,132 (Pamula et al, issued Jun. 28, 2005) discloses a two dimensional EWOD array to control the position and movement of droplets in two dimensions.
Many applications of EWOD technology require that the temperature of liquid droplets be controlled and/or varied. Examples include molecular diagnostics, material synthesis and nucleic acid amplification. The latter generally requires biochemical reagents to be cycled through two or more temperatures. One approach to achieving thermal control is to control the temperature of the entire device and its housing by external means, e.g. a hot plate. This suffers from the disadvantages that the rates of temperature change that can be achieved are generally low, that a long time is required for the whole arrangement to reach thermal equilibrium. Furthermore different droplets cannot simultaneously have different temperatures within the same device.
US20080274513 (Shenderov et al., published Nov. 6, 2008) discloses an alternative approach whereby multiple heating zones within a device are maintained at different temperatures, and the temperature of a droplet is controlled by using electro-wetting to move the droplets between the different zones.
WO2009/003184 (Wu, published Dec. 31, 2008) further discloses how such heating zones may be implemented by mounting heat exchangers on the back surfaces of the lower and upper substrates. A disadvantage of this method is that the thermal resistance between the heat exchangers and the droplets will be relatively large since in general the substrates are fabricated from a poorly thermally conducting material, e.g. glass. This will adversely affect the spatial resolution of the thermal control that can be achieved and also result in a long thermal time constant.
U.S. Pat. No. 7,163,612 (J. Sterling et al., issued Jan. 16, 2007) describes how TFT based electronics may be used to control the addressing of voltage pulses to an EWOD array by using circuit arrangements very similar to those employed in AM display technologies. Such an approach may be termed “Active Matrix Electro-wetting on Dielectric” (AM-EWOD). A disadvantage of U.S. Pat. No. 7,163,612 is that it does not disclose any circuit embodiments for realising the TFT backplane of the AM-EWOD.
WO2010/041214 (Lasance et al., published Apr. 15, 2010) describes a microfluidic device comprising an array of fluidic chambers. Each chamber contains a heater integrated into the substrate which is independently controllable. Each chamber also contains a temperature sensor. WO2010/041214 further describes how integrated electronics may be disposed upon the substrate for driving the heaters and temperature sensors. A disadvantage of WO2010/041214 is that it does not describe any integrated means for moving the fluids between the different chambers of the device.
In view of the afore-mentioned disadvantages associated with conventional EWOD devices, there is a strong need for an EWOD device having prompt, high spatial resolution temperature control with simplified manufacture and reduced cost.